The present invention relates to bone plates and the manner in which they are connected to bone, and more particularly, to locking pegs with extended threads to assist in removing the pegs from bone.
FIG. 1 illustrates a prior art bone plate fixation system including a bone plate 10, non-locking bone screws 20, locking screws 25, and locking pegs 30. Traditional bone screws 20, locking screws 25, and locking pegs 30 are used to fix bone or at least partially connect plates to bone. Unlike traditional bone screws 20, the shafts of locking pegs 30 generally are unthreaded. Locking pegs 30 may be used, for example, in the distal portion of distal radius plates, as illustrated in FIG. 1. The use of multiple non-parallel locking pegs 30 may provide enough local bone-to-plate fixation such that a thread on the shaft of the locking peg 30 is not necessary.
Among other benefits, locking pegs 30 may be inserted quickly because they may be pushed through a pilot hole in the bone without requiring screwing the shaft into the bone. This substantially reduces the time required to insert the locking peg, such that the locking peg need only be pushed into the pilot hole and screwed a few revolutions to activate the locking mechanism between a threaded head of the locking peg and a threaded hole of the bone plate. Furthermore, because locking pegs 30 have unthreaded shafts, the locking pegs have fewer sharp edges than traditional bone screws 20 and pose less of a risk for damage to tissues surrounding the bone, such as the radial cartilage in the wrist joint. Thus, locking pegs 30 may be especially useful when it is desired to place the locking peg 30 very close to a joint surface.
FIGS. 2A-B illustrate steps for explantation (i.e., removal) of locking pegs 30 according to the prior art. Explantation of locking pegs 30 is generally more difficult than explantation of traditional bone screws 20. Because locking pegs 30 have no threading on the shaft, counterclockwise rotation of the locking peg 30 will only disengage the screw head 40 from the bone plate 10. Additional rotation will not provide additional axial force to extract the locking peg 30, as the unthreaded shaft will simply rotate within the bone hole without any translation. Instead, the locking peg 30 must be grasped at the head 40, as illustrated in FIG. 2B, and pulled out of the bone. However, unscrewing the head 40 of the traditional locking peg 30 generally only raises the locking peg 30 by a small amount. Depending on the design of the particular hole in the bone plate 10, it often is difficult to grasp the head 40 of the locking peg 30 with forceps or other devices because the head 40 only protrudes a small distance above the bone plate 10. As a result, surgeons often resort to pulling the locking peg 30 out of the bone by pulling on the bone plate 10. Surgeons may even resort to making an incision in tissue opposite the side of the head 40 of the locking peg 30 to push the locking peg 30 up out of the bone plate 10. Each of these approaches carries risks to the patient.
Therefore, there exists a need for locking pegs that retain the benefits of traditional locking pegs while mitigating issues of difficult removal from the bone.